Dehumidifier schedule

[jsbartley]

I am in Miami fighting summer humidity on my sailboat w no shorepower and limited solar panels. I have a small 12v dehumidifier but can only operate around 8 hrs each day. Temp in closed boat goes from 105 late afternoon to mid 80s at night and early am. What is the best schedule for my dehumidifier timer?

[Sailmonkey]

Not sure why you put this in the opencpn navigation thread........

I’d run the dehumidifier while the sun allows from the solar.

[jsbartley]

Thanks, Sailmonkey for your advice and for pointing out the incorrect thread posting. Tried doing from my phone! Will see if I can correct that!

[thinwater]

Actually, depending on battery capacity and the draw of the unit, consider running either pre-dawn, or maybe 6am - noon. The relative humidity will be less than 50% during the day and near the dew point at night. During the day, the unit will not be able to pull water, at night it will be easy. You want to run the unit at the lowest practical temperature.

[a64pilot]

I moved it to electrical, we all make mistakes

You should not run a dehumidifier, ever when on a boat in hot weather.

The reason is a dehumidifier is an airconditioner, it condenses the water onto the evaporator coil, then moves that cold air over the condenser coil to cool the refrigerant, but what it does is create heat. It’s actually adding heat to the boat as all that work to run the compressor etc is dissipated as heat.

What you want to do is run an airconditioner and exhaust that heat outside of the boat, either by air or water, and enjoy the cooling, maybe you don’t have power except enough to run a small one, and finding one of those that isn’t priced crazy may be the challenge.

An airconditioner is just as efficient as a dehumidifier.
A dehumidifiers best use is Winter where they can add a little nest to the boat.
When we stored our boat in a Marina during the week when I still worked, we ran the AC in Summer and the Dehumidifier in Winter

[a64pilot]

The dehumidifier you almost certainly have is a Peltier plate one, they are horribly inefficient and don’t work very well.
Your answer I’m afraid is going to be a Honda generator and a 5000BTU AC from a home box store.
Honda $1,000, AC can be had for about $150 I think.

[Pizzazz]

The best you can do is not to have a dehumidifier. You can get a compressor dehumidifier drawing around 2-300W that will efficiently dry the air. However, as soon as you open a hatch, the air will quickly become damp again. If you have the hatch closed, your body will produce more humidity. You are better off with either fans or a real Air conditioner which needs a generator. Dehumidifiers work well if you are connected to shore power and you are not on board.

[jsbartley]

Thanks for all of your input (and for reposting this where it belongs!).

Yes, it's an EvaDry which is Peltier-based. I realize the best option for this problem, is a genset with a compressor-based dehumidifier or operating air condictioner, but it's not an option at this time for me. The boat is closed, and needs to remain closed when not in use, given iguanas, rats, etc, on the dock, and heavy summer storms that blow thru. The Evadry fills its reservoir (16 oz) every two days or so if I running it 12 hours a day in two hour increments (two hours on, two hours off), but that is too much draw on house bank and cannot be replaced by a day of sunlight on the two 100W panels. So, I have to cut back the hours, until I put additional panels on the boat.

So, the question is: 1. better to use the dehumidifier or not?, and 2. if yes, and assuming I can only operate 6-8 hours a day, in what time slots should I run it? From the answers above sounds like low temp hours are the best... i.e. late night and dawn.

Again, appreciate the input from everyone. You guys are the best!

[Pizzazz]

It is better to use a fan to move the air. Either install one in the dorades or through a hatch. The fan will do better in your case.

[a64pilot]

Originally Posted by Pizzazz

It is better to use a fan to move the air. Either install one in the dorades or through a hatch. The fan will do better in your case.

I agree, hugely less power draw and should be able to run continuously. And should keep the boat much, much cooler.
I’m not a fan of those Solar vent fans myself though, they are expensive, require permanent installation and don’t seem to last long based on reports I get here.
I’d find a fan that would fit in a hatch and leave it about half open and fit the fan into the opening, half open in case it rains, which it will.

Carafamo ultimate pulls I think .3 amps low, .4 amps on high, I think.

[thinwater]

Originally Posted by jsbartley

Thanks for all of your input (and for reposting this where it belongs!).

Yes, it's an EvaDry which is Peltier-based. I realize the best option for this problem, is a genset with a compressor-based dehumidifier or operating air condictioner, but it's not an option at this time for me. The boat is closed, and needs to remain closed when not in use, given iguanas, rats, etc, on the dock, and heavy summer storms that blow thru. The Evadry fills its reservoir (16 oz) every two days or so if I running it 12 hours a day in two hour increments (two hours on, two hours off), but that is too much draw on house bank and cannot be replaced by a day of sunlight on the two 100W panels. So, I have to cut back the hours, until I put additional panels on the boat.

So, the question is: 1. better to use the dehumidifier or not?, and 2. if yes, and assuming I can only operate 6-8 hours a day, in what time slots should I run it? From the answers above sounds like low temp hours are the best... i.e. late night and dawn.

Again, appreciate the input from everyone. You guys are the best!

I've used Evadry units just as you describe for over a decade onj two different boats. So long as the boat is tight, they work very well. Make sure the bilge is dry and ALL of the vents are closed. You should be able to run it less than that. One boat was a 35-foot catamaran with a LOT more volume.

I rigged a drain hose (1/8" ID) to the sink on each boat. Works well if the sink drain is above the WL and no seacock, as mine have been (multihulls).

Sorry guys, but this actually does work better than fans, and running AC is not an option for a boat with limited power. Remember, he is doing this for storage, NOT while he in on the boat. I often ran it on solar (2 x 85W panels) by regulating the hours. No, the boat will not seem particularly hot inside when you return, because the humidity will be MUCH lower than outside and the unit does not add measurable heat to the boat (watts are too low--simple math).




Sail Delmarva: 100 Best--Chapter 12

[jsbartley]

Thanks for responses.... sooooo, looks like two schools of thought,
1. one with dehumidifiers-a/c of which I can only opt at this time for running my little Peltier (EvaDry) for 3-4 hours during the coolest hours (dawn).
2. the other is with venting cabin air to the outside with a solar-powered hatch-installed fan, which would be replaced by outside air which is up to 20 degrees cooler than the 105 degree air in the boat.
Is that a fair recap?
How about both? During day, hottest air vented and replaced with cooler air, and at night, when the solar powered fan is not operating, the EvaDry could pull some humidity out of the cooler air.... or am I just spinning wheels here? Thanks friends for your patience!

[thinwater]

No, you really don't want to try both. It won't work, at all. Chose one.

[a64pilot]

I don’t think he is doing it for storage? I think he is living aboard?

[jsbartley]

Not for storage or live aboard. The boat is docked 5 min from my house in Coconut Grove, on a seawall. I sail it once or twice a week, and visit the boat to work on it 2-3 more times a week as that is my escape! So, for one reason or another it's getting opened and fully ventilated about every other day.

Maybe dehumidifier is NOT a good option in that scenario, since each time I open it, it becomes invaded by more humid air???

Trying not to "beat a dead horse" here, but if that additional info helps tune the advice, it will be worth it for me! Thanks again.